Ta có : a + b = 1 

=> 2a + 2b = 2 

Ta có : 4a + 2b - (2a + 2b) = 1 - 2

<=> 4a + 2b - 2a - 2b = -1

=> 2a = -1

=> a = -1/2

=> b = 1 - (-1/2)

=> b = 3/2 

\(\hept{\begin{cases}a+b=1\\4a+2b=1\end{cases}}\Rightarrow\hept{\begin{cases}2a+2b=2\\2a+2b+2a=1\end{cases}}\Rightarrow\hept{\begin{cases}2a+2b=2\\2+2a=1\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}2a+2b=2\\2a=-1\end{cases}}\Rightarrow\hept{\begin{cases}2a+2b=2\\a=-\frac{1}{2}\end{cases}}\Rightarrow\hept{\begin{cases}b=\frac{\left(2-2.\frac{-1}{2}\right)}{2}=\frac{3}{2}\\a=\frac{1}{2}\end{cases}}\)

2a - b = 3 => b = 2a - 3.thay vào  4a + 2b = 34  ta đc

4a + 2.(2a - 3) = 34 => 4a + 4a - 6 = 34 => 8a = 40 =>a =  40 : 8 = 5  => b = 2.5 - 3 = 7

vậy a/b = 5/7

1)  \(4x=5y\)\(\Rightarrow\) \(\frac{x}{5}=\frac{y}{4}\)hay  \(\frac{2x}{10}=\frac{y}{4}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

    \(\frac{2x}{10}=\frac{y}{4}=\frac{y-2x}{4-10}=\frac{-5}{-6}=\frac{5}{6}\)

suy ra:  \(\frac{2x}{10}=\frac{5}{6}\) \(\Rightarrow\)\(x=\frac{25}{6}\)

            \(\frac{y}{4}=\frac{5}{6}\)\(\Rightarrow\)\(y=\frac{10}{3}\)

Vậy...

2) lm tương tự

\(\frac{a+1}{2}\)= \(\frac{b+2}{3}\)=\(\frac{c+2}{4}\) và 3a-2b+c=105

áp dụng dãy tỉ số bằng nhau ta có

\(\frac{a+1}{2}\)=\(\frac{b+2}{3}\)=\(\frac{c+2}{4}\)=\(\frac{3\left(a+1\right)-2\left(b+2\right)+c+2}{3.2-2.3+4}\)=\(\frac{3a+3-2b-4+c+2}{3.2-2.3+4}\)=\(\frac{\left(3a-2b+c\right)+3-4+2}{6-6+4}\)=\(\frac{105+1}{4}\)=\(\frac{106}{4}\)=26,5

ta có \(\frac{a+1}{2}\)=26,5 => a+1=26,5x2=53=>a=53-1=52

\(\frac{b+2}{3}\)=26,5=> b+2=26,5x3=79,5=> b=79,5-2=77,5

\(\frac{c+2}{4}\)=26,5=>c+2=26,5x4=106=> c=106-2=104